IT202100025970A1 - “DEVICE FOR ENGAGING/DISENGAGING THE POWER TRANSMISSION BETWEEN THE POWER INPUT AND THE POWER OUTPUT OF A LAWN MOWER AND LAWN MOWER EQUIPPED WITH SUCH DEVICE.” - Google Patents

Description

DESCRIPTION

of the industrial invention entitled:

?Device for engaging/disengaging the power transmission between the power input and the power output of a lawn mower and mower equipped with this device.?

The present invention concerns a device for engaging/disengaging the transmission between the power input and the power output of a lawnmower and lawnmower equipped with this device.

Are devices known in the state of the art capable of allowing the transmission of motion between a power input, that is? a thermal or electric motor or a shaft or another mechanical component that draws power from a third source, and a power output, that is? a mechanical component that makes said power available to the user machine, scaled to the required torque and rotation speed, normally consisting of a shaft possibly also moved by the last toothed wheel of a reducer.

A plug-in system? shown in EP 3216190. And? a sawtooth clutch system composed of two halves, a toothed wheel 23a and a toothed wheel 23b, normally separate but self-engaging when engaged. power to the system. The 23b wheel? integral with a shaft 25 while the toothed wheel 23a is free axially. The operation of the system provides that the power is transmitted from the wheel 21 to the wheel 22 to make it rotate. The aforementioned wheel? equipped with cavities? shaped parts 220 into which profiles 230 obtained on the first toothed wheel 23a are inserted. When is it there? rotation, the profiles 230 are pushed axially due to the onset of an axial component of the force at the point of contact. The induced axial force? such as to overcome the force of a spring 26, bringing the two halves closer together? 23a, 23b of the coupling which close and allow the transmission of motion.

In view of the state of the art, the purpose of the present invention? that of providing a device for engaging/disengaging the power transmission between the power input and the power output of a lawnmower which is different from those known.

In accordance with the present invention, said purpose is achieved by means of a device for engaging/disengaging the power transmission between the power input and the power output of a lawnmower, said device being configured for unilateral power transmission from the power input power to the power output of the lawnmower, characterized by the fact that said device is configured to engage/disengage the power transmission between the power input and the power output automatically, said device comprising:

- A first rotatable element connected to the power input;

- A second rotatable element connected to the power output;

- An idler disposed between said first and said second rotatable elements, said idler being configured to transmit rotation from said first rotatable element to said second rotatable element when said first rotatable element is powered for rotation by said power input and being configured to prevent transmission of rotation between said first and second rotatable elements in the absence of power for rotation by said power input. Thanks to this invention? Is it possible to provide a power transmission clutch/disengagement device between the power input and power output of a lawn mower that allows power transmission in one direction only, i.e.? from the power input towards the power output. Can you? clearly if necessary be installed inverted, allowing the transmission of motion in the opposite direction.

The aforementioned device facilitates the movement of the lawnmower, for example a pedestrian lawnmower equipped with a small electric or mechanical traction, by a user, since a certain power is made to flow from a primary source up to the wheels in the form of a suitable torque and rotation speed. The adaptation and the flow of power are conveyed by the drive unit itself. In fact, if the traction unit were without the aforementioned device in accordance with the invention, there would be an uninterruptible motion transmission chain between all the internal transmission chain members of the traction, from the power input of the latter up to its exit, here coinciding with the axis of the lawnmower wheels. It would not be possible in any way to separate the motion of the lawnmower wheels from that of the power input. If there? is acceptable during the advancement phase of the lawnmower, that is? in normal use of the same, isn't it? instead in the case in which the power input is stopped on command, for example to drag the lawnmower backwards or to push it manually. In fact, since the wheels are not free from the other components of the transmission chain, they rotating due to contact with the ground? they will have to move all the remaining components of the chain itself, overcoming their friction/resistance and making the user feel a useless effort for the purposes of the action he is carrying out.

This additional effort? present precisely by virtue? of the establishment of a reversed flow of power, in this case from the wheels to the primary source of power, whose appearance we therefore want to avoid.

The characteristics and advantages of the present invention will be evident from the following detailed description of one of its practical embodiments, illustrated by way of non-limiting example in the attached drawings, in which:

figure 1? an exploded view of a traction where a power input, a power output and a device for engaging/disengaging the power transmission between the power input and the power output of a lawnmower in accordance with the present invention are represented;

figures 2 and 3 show more? in detail the device for engaging/disengaging the transmission between the power input and the power output of a lawnmower in accordance with a first embodiment of the present invention;

figure 4 schematically shows the device of figures 2 and 3 in the coupling phase;

figure 5 schematically shows the device of figures 2 and 3 in the disengagement phase;

figure 6 shows the device of figures 2 and 3 in the initial condition;

figures 7 and 8 show the device of figure 6 in the initial (figure 7) and final (figure 8) engagement phases;

figures 9 and 10 show the device of figure 6 in the initial (figure 9) and final (figure 10) disengagement phases;

figures 11 and 12 show more? in detail the device for engaging/disengaging the transmission between the power input and the power output of a lawnmower in accordance with a second embodiment of the present invention;

figure 13 schematically shows part of the device of figures 11 and figure 14 schematically shows the device of figures 11 and 12 in the coupling phase, with the triangles of the forces that are generated during the coupling phase highlighted engagement, triangles valid for any realization of the device;

figure 15 shows more? in detail the device of figures 11 and 12;

figures 16-18 show the device of figure 15 in the initial (figure 16), intermediate (17) and final (figure 18) engagement phases;

figures 19 and 20 show the device of figure 16 in the initial (figure 19) and final (figure 20) disengagement phases.

In figure 1? shown is a part of a lawnmower, in particular a traction unit, comprising a power input device 100, a power output device 200 and the device 1 for engaging/disengaging the transmission between the power input device 100 and the device of power output 200. In figure 1 ? shown as 100 power input device, an electric motor but can? be made up, alternatively, of a heat engine or a shaft capable of receiving power in turn from another source. Still in figure 1? shown as power output device 200, a shaft 201 provided with a gear wheel 202 and a reduction gear 300 for its movement.

Device 1 ? inserted inside the traction unit, in an intermediate position between the power input device 100 and and the power output device 200, in particular? positioned before the gear reduction stages which are necessary to multiply the input torque up to the required output values from the lawnmower where the traction unit is installed; however, device 1 can? occupy any position between entrance 100 and exit 200.

Device 1 ? configured to engage/disengage power transmission between power input 100 and power output 200 automatically. As better visible in figures 2 and 3 according to a first embodiment of the invention, the device 1 comprises a first rotatable element 12 connected to the power input 100, a second rotatable element 11 connected to the power output 200 and an idle element 13 arranged between said first and second rotatable elements. The crazy element 13 ? configured to transmit rotation from the first rotatable element 12 to the second rotatable element 11 when the first rotatable element is powered for rotation by power input 100; the crazy element 13 ? configured to prevent the transmission of rotation between the first and second rotatable elements in the absence of power for rotation from the power input.

As visible in figures 2 and 3, the second rotatable element 11? of the wheel type and ? integral with the first gear wheel of the reducer 300 which moves the power output device 200. The element 11 can? also be connected directly to the shaft 201 of the device 200 if the reduction unit is absent from the output device 200; element 11 ? cable inside to house the other elements of the device 1.

The first rotatable element 12? preferably a lobed cam, still preferably a trilobed cam, connected in rotation to the power input device 100, preferably integral with the power input device, thus being able to rotate at the same speeds? angles of the same device 100 or different if integral with elements that reduce or amplify the rotation of the device 100.

The idle element 13 includes a circular support 131, which is also hollow inside to house the other elements of the device 1. The element 13 is normally neutral with respect to both the wheel element 11 and the trilobal cam 2, and is destined to remain so as long as? some power flow does not enter device 1 from the power input side. Preferably element 13? such that it can be placed inside the hollow part of the wheel element 11.

The circular support 130 contains elements of the C-type 14, pivoted inside the support 130 via pins or pins 144 and, when at rest, completely contained in special compartments 145 obtained in the same support 130. The C-shaped elements 14, also called engagement pegs are designed to engage with specific protuberances or protrusions or internal geometries 15 of the wheel element 11 when a power flow is established from the input 100 towards the output 200, guaranteeing engagement and transmission of motion. As visible in figures 2 and 3, the protuberances 15 extend predominantly radially with a profile that develops on a plane perpendicular to the rotation axis A of the trilobal cam 12 and the C-shaped elements 14 are pivoted on the support 130 in such a way to be mobile on a plane orthogonal to the same axis. The circular support 13 ? also provided with holes 17 on its side wall 18 to allow the passage of the ends? free 141 of the C-shaped elements 14 outside of the element 13.

There are also present, inside the circular support 131, compression springs 16 whose task is to that of facilitating the return of the C-shaped elements 14 into the special spaces 145 of the element 13 when the power flow from the input to the output is interrupted, thus allowing the disengagement action. The device 1 includes as many springs as there are C-shaped elements 14, one for each C-shaped element. Each spring 16 has an end? integral with the internal part of the side wall 18 of the support 130 and the other integral with the internal part of the C of the C-shaped element 14, thus generating that action on the C-shaped element necessary to make it re-enter the aforementioned spaces during disconnection. In the particular case in which only two elements of engagement are present, can? a single spring capable of acting simultaneously on both engagement elements is sufficient.

Element 11 is provided with a side wall 150 suitable for assisting said elastic means in disengaging the C-shaped elements 14 from the protrusions 15 in the absence of power supply for rotation from the power input; the wall 150 preferably has portions 151 with a curvilinear shape between two internal projections 15. Each internal projection 15 of the element 11 includes a wall with a specific inclination 152 on which the end abuts. free 141 of the C-shaped element 14. Each curvilinear portion 151 has an increasing distance from the center, in which the rotation axis A passes, from the extremity more? inside of a projection 15 up to the end? more? external of the next projection 15 following an anti-clockwise trend

Device 1 in use? configured with the element 13 inserted into the wheel element 11, as visible in figures 6-10.

The transmission engagement/disengagement device 1 between the power input device 100 and the power output device 200? configured so as to allow the transmission of motion in only one clockwise or anti-clockwise direction and only from device 100 to device 200 and not vice versa.

In general, the device 1 for engaging/disengaging the transmission between the power input device 100 and the power output device 200 engages or engages automatically and autonomously if energy arrives from the power input device 100 in the form of of a torque at a certain rotation speed. The device remains engaged as long as energy continues to flow from the power input 100, thus allowing the transmission of motion towards the power output device 200. The device 1 disengages or disengages autonomously and automatically the instant this energy flow from the power input occurs interrupt itself, thus also interrupting the possibility? of any motion transmission towards the exit. In the absence of energy from the input, device 1 remains disengaged, even if the power output is in motion induced by the user. Aren't you? therefore no reverse flow of power from the output to the input, that is? from device 200 to device 100.

In particular, from a rest phase (figure 6) to the engagement phase (figure 7) an energy flow is activated from the power input device 100. The trilobal cam 12, integral with the power input device 100, begins to rotate. At the same time the wheel element 13 remains stationary, due to its own inertia and thanks to the balancing of the moments due to all the forces in play, i.e. the force of the springs 16, the actions on the support pins 144 of the C-shaped elements 14 and the friction (as better visible in figures 4 and 5). In this way the lobes of the cam 12, which rotates clockwise, act on special profiles 143 made on the C-shaped elements 14, applying a force to make them rotate in accordance with a direction, for example anti-clockwise with respect to their support pin 144 and overcoming the ?contrasting action of the springs 16. In this way the ends? free spaces 141 of the C-shaped elements 14 protrude from the respective holes 17 of the side wall 18.

At the same time the element 13 begins to rotate as the configuration of the moments that govern its rotation changes and drags with it? in the rotation also the C 14 elements, whose ends? free 141 slide on the side wall 150 of the wheel element 11, which is still stationary, until it comes to rest on the internal protuberances 15 (figure 8). When ? once this configuration is reached, all the components lock together, becoming one, integral with each other: the transmission of motion becomes effective.

The disengagement function occurs automatically when the flow of energy from the power input device 100 is interrupted (Figure 9). Indeed, when will there? occurs, the three-lobed cam 12 stops, as it is integral with the power input device 100. The three-lobed cam 12 stops acting on the C-shaped elements 14, allowing them to return from the hole 17. In fact, the wheel element 11 continues to rotate why? connected with form coupling (gears or - where absent - keying on the output member) with the wheels of the machine, which by inertia tends to proceed in its motion also pulling the wheel element 11. Once the action of the trilobate cam 12, both the action of the side wall 18 of the wheel element 11 combined with the anti-clockwise rotation of the same wheel element 11 and both by the release action of the springs 16, the C-shaped elements 14 are pushed inwards of element 13 in their special compartments (figure 10). The disengagement? completed.

The springs 16 help to avoid unwanted engagement when there is no energy flow from the power input: for example for jolts, vibrations etc. This, regardless of the direction of travel of the machine.

As better visible in figures 11-20 according to the second embodiment of the invention, the device 1 comprises a first rotatable element 120 connected to the power input 100, a second rotatable element 110 connected to the power output 200 and a idle element 130 arranged between said first and second rotatable elements. The crazy element 130 ? configured to transmit rotation from the first rotatable member 120 to the second rotatable member 110 when the first rotatable member ? powered for rotation by power input 100; the crazy element 13 ? configured to prevent rotation transmission between the first and second rotatable elements in the absence of rotation power from the power input.

As visible in figures 11-20, the second rotatable element 110? of the wheel type and ? integral with the first gear wheel of the reducer 300 which moves the power output device 200. The element 110 can? also be connected directly to the shaft 201 of the device 200 if the reduction unit is absent from the output device 200; element 110 ? cable inside to house the other elements of the device 1.

The first rotatable element 120 ? preferably a lobed cam, still preferably a trilobed cam, integral with the power input device 100, with respect to which ? connected integrally to the rotation, therefore being able to rotate at the same speeds? corners of the same device 100.

The idle element 130 includes a circular support 132, also hollow inside to house the other elements of the device 1. The element 130 is normally neutral with respect to both the wheel element 110 and the trilobal cam 120, and is destined to remain so as long as? some power flow does not enter device 1 from the power input side. Preferably element 130? such that it can be placed inside the hollow part of the wheel element 110.

The circular support 132 contains elements of the I-type 140, arranged inside special compartments 147 obtained in the support 132 and, when at rest, completely contained in said special compartments 147. The I-shaped elements 140, also called the engagement pegs, they are capable of engaging with specific protuberances or protrusions or internal geometries 155 of the wheel element 110 when a power flow is established from the input 100 towards the output 200, guaranteeing the engagement and transmission of the motion. As visible in figures 11 and 12, the protuberances 155 extend predominantly radially with a profile that develops on a plane perpendicular to the axis A of rotation of the trilobate cam 120 and the I-shaped elements 140 are arranged on the support 132 in such a way to be mobile on a plane orthogonal to the same axis. The circular support 132 ? also provided with holes 170 on its side wall 180 to allow the passage of the ends? free 146 of the elements 140 outside the element 130.

There are also present, inside the circular support 132, compression springs 160 whose task is that of facilitating the return of the elements 140 into the special spaces 147 of the element 130 when the power flow from the input to the output is interrupted, thus allowing the disengagement action. The device 1 comprises as many springs as there are elements 140, one for each element 140. Each spring 160 has an end? integral with the internal part 148 of the compartment 147 of the support 130 and the other integral with the body, preferably in the central part, of the I-shaped element 140, thus generating that action on the element 140 necessary to make it re-enter the aforementioned compartment 147 during disengagement . In the particular case in which only two elements of engagement are present, can? a single spring capable of acting on both simultaneously is sufficient.

Element 110 is provided with an internal lateral wall 156 suitable for assisting said elastic means 160 in disengaging the elements 140 from the protrusions 155 in the absence of power supply for rotation from the power input; the wall 156 preferably has portions 157 with a curvilinear shape between two internal projections 155. Each internal projection 155 of the element 110 includes a wall with a specific inclination 158 on which the end abuts. free 146 of the element 140. Each curvilinear portion 157 has an increasing distance from the center, through which the rotation axis A passes, from the extremity more? internal of a projection 155 up to the end? more? external of the next projection 155 following an anti-clockwise trend

Device 1 in use? configured with the element 130 inserted into the wheel element 110, as visible in figure 15.

The transmission engagement/disengagement device 1 between the power input device 100 and the power output device 200? configured so as to allow the transmission of motion in only one clockwise or anti-clockwise direction and only from device 100 to device 200 and not vice versa.

In general, the device 1 for engaging/disengaging the transmission between the power input device 100 and the power output device 200 engages or engages automatically and autonomously if energy arrives from the power input device 100 in the form of of a torque at a certain rotation speed. The device remains engaged as long as energy continues to flow from the device 100, thus allowing the transmission of motion towards the power output device 200. The device 1 disengages or disengages autonomously and automatically the instant this flow of energy from the power input is interrupted, in this way thus also interrupting the possibility? of any motion transmission towards the exit. In the absence of energy from the input, device 1 remains disengaged, even if the traction/gearmotor output is in motion induced by the user. Aren't you? therefore no reverse flow of power from the output to the input, that is? from device 200 to device 100.

In particular, in the engagement phase (figure 17) after the rest phase (figure 16) an energy flow is activated from the power input device 100. The three-lobed cam 120, integral with the power input device 100, begins to rotate. At the same time the wheel element 130 remains stationary, due to its own inertia and thanks to the balancing of the moments due to all the forces in play, that is? the force of the springs 160 and the friction. In this way the lobes of the cam 120, which rotates clockwise, act on the lower parts 149 of the elements 140 by applying a force to make them slide orthogonally with respect to the rotation axis A of the cam 120 (as visible in figures 13 and 14), winning the contrasting action of the springs 160. In this way the ends? free holes 146 of the elements 140 protrude from the respective holes 170 of the side wall 180 (figure 17).

At the same time the element 130 begins to rotate as the configuration of the moments that govern its rotation changes and drags with it? in the rotation also the elements 140, whose ends? free 141 slide on the side wall of the wheel element 110, which is still stationary, until it comes into contact with the internal protuberances 155 (figure 18). When ? once this configuration is reached, all the components lock together, becoming one, integral with each other: the transmission of motion becomes effective.

The disengagement function occurs automatically when the flow of energy from the power input device 100 is interrupted (Figure 19). Indeed, when will there? happens, the trilobal cam 120 stops, as it is integral with the power input device 100. The trilobal cam 120 stops acting on the elements 140, allowing them to return from the hole 170. In fact, the wheel element 110 continues to rotate because? connected with form coupling (gears or - where absent - keying onto the output member) with the wheels of the machine, which by inertia tends to proceed in its motion also pulling the wheel element 110. Once the action of the trilobate cam 120, both the action of the side wall 180 of the wheel element 110 combined with the anti-clockwise rotation of the same wheel element 110 and both by the release action of the springs 160, the elements 140 are pushed towards the inside of the appropriate 147 rooms (figure 20). The disengagement? completed.

The 160 springs help avoid unwanted engagement when there is no energy flow from the power input: for example for jolts, vibrations etc. This, regardless of the direction of travel of the machine.

The profiles of the trilobe cams are designed so that the direction of the force F imparted to the C-element 14 or to the I-element 140 changes slightly from the beginning of the engagement movement (F1) to an intermediate phase (F2) until its end (F3) like this? to have a lower torque required during the beginning of the engagement movement, as visible in figure 14. In this way a low load is achieved. seen from the motor at the beginning of the engagement while a transmission torque is ensured at the end of the engagement movement. In fact, the tangential force Ftang between the trilobal cam and the C element 14 or the I element 140 grows from zero to its maximum value F3,tang. The zero or almost zero value of the tangential force at the beginning of the engagement movement facilitates the same movement since the C-element 14 or the I-element 140 slides on the profile of the lobe with low friction.

In particular, the profiles 143 made on the mobile C-shaped elements have a specific shape to be able to interact with the profile of the cam 12 with which they are in contact in such a way as to minimize the resistant torque seen by the cam during the very first phase of engagement and gradually to make it grow until it allows the transmission of rotation once engagement is complete.

That is, when the cam 12 begins to rotate, there is no possibility? to generate at the cam?element interface any component of tangential force that can be configured as resistant, so that? the moment of resistance seen by the cam is almost zero. This fact allows the primary power source that moves the mechanism not to see sudden increases in resistant torque at the beginning of the engagement, thus avoiding sudden increases in power demand which could lead to problems such as vibrations, anomalous functioning or even shutdown of the machine.

Similarly the two profiles? both on the cam side and on the C or I element side - they develop in such a way as to be able to exchange a gradually increasing component of tangential force as the engagement phase proceeds from the beginning until complete engagement. Are you? therefore possibility? of motion transmission, and the power source consequently sees a resistance torque that gradually increases until complete engagement.

This dynamic effect corresponds to a certain conformation of the force triangles that must be able to be generated at the cam-moving element interface.

With reference to fig.14, it is indicated with:

- F1 is the resultant of the force exchanged between the cam and the I-shaped element at the beginning of the engagement,

- F2 the resultant of the force exchanged between the cam and the I-shaped element in the intermediate phase of the engagement,

- F3 the resultant exchanged between the same components when fully engaged, - Ftang,1, Ftang,2 and Ftang,3 the respective tangential components with respect to the center of rotation lying on the A axis of the cam (the tangential force Ftang,1 is not? indicated in figure 14 as null).

The resulting F1 must pass through the center of rotation of the cam like this? to have in ideal conditions a zero tangential component Ftang,1; similarly F3 categorically must not comply with this requirement, as a component Ftang,3 ? necessary for the transmission of motion. Therefore this resulting F3 must form a certain angle with the straight line passing through the contact point and the center of rotation of the cam. This angle, to make the engagement movement fluid, must gradually increase from approximately 0 to a maximum value proceeding from the beginning to the end of the rotation.

The two coupled profiles are therefore designed in order to obtain the above. In particular:

- at the beginning of the engagement: the straight line normal to the two surfaces and passing through the cam-element contact point must lie on a plane containing the rotation axis of the cam 12. Since? the resultant of the exchanged forces has a direction parallel to said normal line, what? it means that in ideal conditions there is no arm with respect to the cam axis, and therefore it is not possible? generate any resisting moments.

- at the end of the engagement: the straight line normal to the two surfaces passing through the cam-element contact point must lie on a plane not containing the rotation axis A of the cam 12 and having a certain distance from this which serves as the necessary arm for generate the moment that must be transmitted.

From what has been described it can be seen that the engagement/disengagement device during the engagement phase has a conformation of the triangles of the forces between the cam 12 and the C-shaped mobile element suitable for containing the resistant torque seen from the power input in the initial phase of the ?engagement.

Claims (11)

1. Device for engaging/disengaging the power transmission between the power input (100) and the power output (200) of a lawn mower, said device being configured for unidirectional transmission of power from the power input to the output of power of the lawnmower, characterized by the fact that said device is configured to engage/disengage the power transmission between the power input and the power output automatically, said device comprising: - A first rotatable element (12, 120) connected to the power input; - A second rotatable element (11, 110) connected to the power output; - An idler element (13, 130) disposed between said first and said second rotatable elements, said idler element being configured to transmit rotation from said first rotatable element to said second rotatable element when said first rotatable element is powered for rotation by said power input and being configured to prevent transmission of rotation between said first and second rotatable elements in the absence of power for rotation by said power input. 2. Device according to claim 1, characterized in that said first rotatable element (12, 120) is a lobed cam, said idle element includes a plurality? of further mobile elements (14, 140), each further mobile element of said plurality? of further mobile elements (14, 140) being associated (144) with a support (131, 132) of said idle element and being moved by said lobed cam for engagement with an internal protrusion (15, 155) of a plurality ? of internal protrusions of said second rotatable element when said first rotatable element? powered for rotation by said power input. 3. Device according to claim 2, characterized in that the further mobile elements of said plurality? of further mobile elements are rotatable elements (14), each rotatable element of said plurality? of further revolving elements (14) being pivoted (144) for rotation on the support (130) of said idle element and being moved by said lobed cam for engagement with an internal protrusion (15) of a plurality? of internal protrusions of said second rotatable element when said first rotatable element? powered for rotation by said power input. 4. Device according to claim 2, characterized in that the further mobile elements of said plurality? of further mobile elements are sliding elements (140), each sliding element of said plurality? of further sliding elements (140) being arranged for sliding in a special space (147) of said support (130) of said idle element and being moved by said lobed cam (120) for engagement with an internal protrusion (155 ) of a plurality? of internal protrusions of said second rotatable element when said first rotatable element? powered for rotation by said power input. 5. Device according to claims 3 and 4, characterized in that said idle element comprises a plurality? of elastic means (16, 160), each configured to disengage each further element from the corresponding internal protrusion of said second rotatable element in the absence of power for rotation from said power input. 6. Device according to claim 5, characterized in that said second rotatable element (11, 110) is shaped so as to assist said elastic means in disengaging said further elements from said protrusions of said second rotatable element in the absence of power supply for rotation from said power input. 7. Device according to claim 6, characterized in that said second rotatable element (11, 110) comprises a lateral wall (150, 156) provided with curvilinear portions (151, 157) at an increasing or decreasing distance from the center between an internal protrusion (15, 155) and its subsequent (15, 155) of said plurality? of internal protrusions. 8. Device according to claims 3 and 5, characterized in that each further rotatable element (14) of said plurality? of further rotating elements (14) ? of the C type having one?extremity? hinged on said support and an? extremity? free (141) capable of engaging with the corresponding internal protrusion, said support (130) includes a circular side wall provided with a plurality of of holes (17) each for the exit of said end? free (141) of the further revolving element, each elastic means being arranged between said side wall of the support and the internal part of the C of the further revolving element. 9. Device according to claims 4 and 5, characterized in that each further sliding element (14) of said plurality? of further sliding elements (14) ? of the I type having one?extremity? (149) designed to engage with one lobe of the lobed cam and the other end? (146) designed to engage with the corresponding internal projection (155), said support (130) includes a circular side wall (180) provided with a plurality of of holes (170) each for the exit of said end? free (146) of the further sliding element, each elastic means (160) being arranged inside each compartment (147) of the support and connected between a central part of the further sliding element and the final part (148) of the compartment. 10. Device according to claim 2, characterized by the fact of generating a conformation of the triangles of the forces between said lobed cam (12, 120) and each further mobile element of said plurality? of further mobile elements (14, 140) designed to contain the resistant torque seen from the power input in the initial phase in which said first rotatable element is powered for rotation by said power input. 11. Lawn mower comprising a power input device (100), a power output device (200) and a power transmission engagement/disengagement device (1) between the power input device and the power output device. power as defined in any of the preceding claims.